The present invention relates to a brushed direct-current motor and a coil winding method for the direct-current motor, and a method for manufacturing the direct-current motor.
A conventional brushed direct-current motor is disclosed in, for example, Japanese Laid-Open Patent Publication No. 2009-27829. The direct-current motor includes a cylindrical yoke having six magnetic poles, an armature rotationally provided inside the yoke, and a commutator, which rotates integrally with the armature. An iron core of the armature includes nine teeth. Each tooth has two coils, which are wound in different winding directions. The commutator includes eighteen commutator pieces, which are arranged in a rotation direction. The winding start end and the winding finish end of the corresponding coil are hooked around each commutator piece. Also, the commutator pieces having the same potential are short-circuited by an equalizer. Two brushes slide against the commutator pieces. Magnetic field is generated on the coils by supplying electricity to the coils via the brushes. The armature is rotated by magnetic attraction and repulsion caused between the magnetic field of the coils and the magnetic poles of the yoke.
In general, the direct-current motor including the direct-current motor of the above publication may be desired to have higher output. In this case, current supplied to the direct-current motor may be increased. However, when current is increased in the direct-current motor of the above publication, decrease in the life of the brushes becomes a concern. That is, since the current loaded on each brush is increased, electrical wear caused by commutation sparks might be undesirably promoted. Also, the greater the amount of supplied current becomes, the greater the diameter of the equalizer needs to be set. Therefore, the space for arranging the equalizer is not easily ensured. As described above, there is a room for improvement in the direct-current motor of the above publication in the aspect of increasing the output.